1. Field of the Invention
The present invention relates to a process for manufacturing a layer of a golf ball. More specifically, the present invention relates to a process for reaction injection molding a layer of a golf ball.
2. Description of the Related Art
Reaction injection molding (“RIM”) is a process used to make golf ball components, such as one-piece balls, covers, cores, and inner layers. Highly reactive liquids are injected into a closed mold, mixed usually by impingement and/or mechanical mixing in an in-line device such as a “peanut mixer”, and polymerized primarily in the mold to form a coherent, molded article. When used to make a thermoset polyurethane or polyurea component, RIM usually involves a rapid reaction between two types of reactants: (a) a polyol or other material with an active hydrogen, such as a polyfunctional alcohol or amine (hereinafter referred to as “polyol” or “POLY”); and (b) an isocyanate-containing compound (hereinafter referred to as “isocyanate” or “ISO”). The reactants are stored in separate tanks prior to molding and maybe first mixed in a mix-head upstream of a mold and then injected into the mold. The liquid streams are metered in the desired weight to weight ratio and fed into an impingement mix-head, with mixing occurring under high pressure, e.g., 1500 to 3000 pounds per square inch (“psi”). The liquid streams impinge upon each other in the mixing chamber of the mix-head and the mixture is injected into the mold. One of the liquid streams typically contains a catalyst for the reaction. The reactants react rapidly after mixing to gel and form polyurethane or polyurea polymers.
RIM offers several advantages over conventional, injection and compression molding techniques for producing golf products and/or equipment. For example, in the RIM process, the reactants are simultaneously mixed and injected into the mold, forming the desired component. In conventional techniques, the reactants must first be mixed in a mixer separate from the molding apparatus, then added into the apparatus. In such a process, the mixed reactants first solidify and must later be melted in order to properly mold the desired components, etc.
Additionally, the RIM process requires lower temperatures and pressures during molding than injection or compression molding. Under the RIM process, the molding temperature is maintained from about 90 to about 180° F., and usually at about 100–160° F., in order to ensure proper injection viscosity. Compression molding is typically completed at a higher molding temperature of about 320° F. (160° C.) while injection molding is completed at an even higher temperature range of 392–482° F. (200–250° C.). Molding at a lower temperature is beneficial when, for example, the cover is molded over a very soft core so that the very soft core does not melt or decompose during the molding process.
Moreover, the RIM process creates more favorable durability properties in a golf ball component than conventional techniques. For example, a golf ball cover produced by a RIM process has a uniform or “seamless” cover in which the properties of the cover material in the region along the parting line are generally the same as the properties of the cover material at other locations on the cover, including at the poles. The improvement in durability is due to the fact that the reaction mixture is distributed uniformly into a closed mold. This uniform distribution of the injected materials reduces or eliminates knit-lines and other molding deficiencies which can be caused by temperature differences and/or reaction differences in the injected materials. The RIM process results in generally uniform molecular structure, density and stress distribution as compared to conventional injection molding processes, where failure along the parting line or seam of the mold can occur because the interfacial region is intrinsically different from the remainder of the cover layer and, thus, can be weaker or more stressed.
Furthermore, the RIM process is relatively faster than conventional techniques. In the RIM process, the chemical reaction usually takes place in under 5 minutes, typically in less than two minutes, sometimes in under one minute and, in many cases, in about 30 seconds or less. The demolding time may be 10 minutes or less. The molding process for the conventional methods itself typically takes about 15 minutes. Thus, the overall speed of the RIM process makes it advantageous over the injection and compression molding methods.
Several patents disclose the use of RIM utilized for golf balls. One of the earliest disclosures of RIM is U.S. Pat. No. 5,356,941 to Sullivan et al., for Game Balls having Improved Core Compositions, which discloses the use of RIM.
Further discloses are set forth in U.S. Pat. No. 6,803,119 to Sullivan et al., for a Multi-Layer Golf Ball, and U.S. Pat. No. 6,287,217 to Sullivan et al., for Multi-Layer Golf Ball, both which disclose the use of a BAYFLEX RIM polyurethane as a cover for a golf ball.
A further disclosure is set forth in U.S. Pat. No. 6,290,614 to Kennedy III et al., for a Golf Ball Which Includes Fast-Chemical-Reaction-Produced Component And Method Of Making Same, which discloses a RIM process in which the temperature is 90–180° F., and the pressure is 200 pounds per square inch (“psi”) or less, and the processing time is 10 minutes or less, and preferably 30 second or less. This patent further discloses that the mix head pressure is between 1500 to 3000 psi.
A further disclosure is set forth in U.S. Pat. No. 6,533,566 to Tzivanis et al., for an Apparatus For Making A Golf Ball, which discloses a turbulence inducing mold for a RIM process.
A further disclosure is set forth in U.S. Pat. No. 6,290,614 to Kennedy II et al., for a Multi-Layer Golf Ball, which discloses a RIM system utilized for a cover of a golf ball.
Another disclosure is U.S. Pat. No. 6,309,313 to Peter, for a Low Cost, Resilient, Shear Resistant Polyurethane Elastomers For Golf Ball Covers, which discloses using RIM at temperatures of 120–250° F.
Yet a further disclosure is set forth in U.S. Pat. No. 6,645,088 to Wu et al., for Reaction Injection Moldable Compositions, Methods For Making Same, And Resultant Golf Articles, which discloses the use of a material with a viscosity less than 20,000 cPs, and an injection pressure less than 2500 psi.
Yet a further disclosure is set forth in U.S. Pat. No. 6,663,508 to Keller et al., for Multi-Layer Golf Ball With Reaction Injection Molded Polyurethane Component, which discloses the use of a BAYFLEX MP-10,000 RIM system which operates at 10–5 mmHg at 77° F. and has a molecular weight of 600–700.
Yet a further disclosure is set forth in U.S. Pat. No. 6,685,579 to Sullivan, for Multi-Layer Cover Polyurethane Golf Bal, which discloses the use of a RIM with a material having a viscosity up to 200 cPs and pressures of 2000 to 2500 psi.
Yet a further disclosure is set forth in U.S. Pat. No. 6,716,954 to Keller et al., for a Golf Ball Formed From A Polyisocyanate Copolymer And Method Of Making Same, which discloses the use of DESMODUR HL material which has a NCO content of 10–11%.
A further disclosure is set forth in U.S. Pat. No. 6,755,634 to Tzivanis et al., for an Apparatus For Forming A Golf Ball With Deep Dimples, which discloses an apparatus capable of using RIM at temperatures of 50–250° F., pressures of 100 psi or less, and an impingement pressure of 150–195 bars.
A further disclosure is set forth in U.S. Pat. No. 6,787,091 to Dalton et al., for a Reaction Injection And Compression Molding Of A Golf Ball, which discloses a reaction injection compression molding RCIM process which operates at an impingement head pressure of 1000 to 5000 psi.
Another disclosure is U.S. Patent Publication Number 2002/0016435 to Simonutti et al., for a Method OF Making A Golf Ball Product From Fast-Curing Reaction Injection Molded Polyurethane, which discloses a RIM process with an isocyanate temperature of 100–130° F., a polyol temperature of 100–130° F., a raw material tank pressure of 40–80 psi, an isocyanate pressure of 1000–3000 psi, polyol pressure of 1000–3000, mold temperature of 130–200° F., and an inject time of less ten seconds.
The term “demold time” generally refers to the mold release time, which is the time span from the mixing of the components until the earliest possible time at which the part may be removed from the mold. At that time of removal, the part is said to exhibit sufficient “green strength.” The term “reaction time” generally refers to the setting time or curing time, which is the time span from the beginning of mixing until the time at which the product no longer flows. Further description of the terms setting time and mold release time are provided in the “Polyurethane Handbook,” edited by Gunter Oertel, Second Edition, ISBN 1–56990-157-0, herein incorporated by reference in its entirety.
Although RIM has been widely used to mold large parts, it has only recently begun to be used in molding small parts, such as golf balls and golf ball components. One challenge is the relatively small shot size associated with such small parts. The small shot size demands that precise amounts of the two reactants be mixed thoroughly and consistently throughout the shot, When the amount of either reactant changes or the degree of mixing changes, the rate at which the part's hardness develops will also change and the final part hardness may be undesirable. These inferior material properties can affect, for example, a golfball's susceptibility to damage when removing the ball from the mold and the toughness of a finished golf ball in resisting scuff damage when struck by a golf club.
Another challenge is ensuring consistency in the finished product over several shot operations. Because the shot size is so small, even small changes in conditions affecting either the reactants or the RIM process itself can change the quality of the finished product.
Although quality control techniques are known, they are especially difficult to apply to golf ball components. For example, at the demold time, it is difficult to determine the quality of a RIM-produced golf ball; the earliest time when the quality can be determined is approximately 1 hour after demolding. Even then, test results may change 12 to 24 hours later as the RIM material continues to cure. Destructive testing destroys the ball and entails extra costs which must be passed on to the consumer. Balls where the mixing was poor or the mix ratio was incorrect may look and feel identical to balls with acceptable quality. As a result of the extra time incurred in detecting defective balls, a large run of unacceptable golf balls may be produced. Hence, new methods for controlling the RIM manufacturing of golf products, such as golf balls and/or components thereof, are desired.